Here is a guide to judging the condition of marbles . . .
Measure the marble using 1/8th of an inch graduations. Use a caliper or template of circles.
Akro Agate Sizing
Diameter Size Rating
1/2 inch 000
9/16 inch 00
5/8 inch 0
11/16 inch 1
3/4 inch 2
13/16 inch 3
7/8 inch 4
15/16 inch 5
1 inch 6
1 1/16inch 7
1 1/8 inch 8
Conditions: From The Marble Collectors Society of America
Mint: Unmarred and in original condition. The best possible condition with clear surfaced marble
Good: The second highest classification. Refers to clear surface with only a few minor dings or slightly cloudy surface. Other terms used to discribe this condition are very good or almost mint.
Collectible: May have some small chips, dings and cloudiness: however, the core of the marble must be easily seen.
Poor: Many deep chips, dings and badly clouded surface. May also have internal fractures.
Polished: Marbles that have been polished to get out the dings and chips. If done right the marble can look like mint condition again. However, to most collectors these are not as valuable as original condition, and probably rate no better than good condition.